Exposure apparatus and device manufacturing method for projecting light from a secondary light source onto a mask or pattern

ABSTRACT

An exposure apparatus includes a light source, first, second and third optical integrators disposed along an optical axis, for receiving light from the light source, each of the integrators having lens elements arrayed in a direction perpendicular to the optical axis, a first condensing optical system for directing, onto the third optical integrator, light passed through the first and second optical integrators, to form a secondary light source through the third optical integrator, a device for relatively shifting the second optical integrator relative to the first optical integrator, in the direction perpendicular to the optical axis, a second condensing optical system for receiving light from the secondary light source and directing the light to a mask, and a projection optical system for projecting an image of a pattern of the mask irradiated with the light from the secondary light source onto a substrate. Also disclosed are device manufacturing methods in which light, passed through first and second lens arrays, which are disposed along an optical axis, form a secondary light source and a device pattern is illuminated with light from the secondary light source whereby the device pattern is transferred to a substrate.

This application is a continuation of application Ser. No. 08/081,194,filed Jun. 25, 1993, now U.S. Pat. No. 5,459,547.

FIELD OF THE INVENTION AND RELATED ART

This invention relates to an illumination device and, more particularly,an illumination device suitably usable in an exposure apparatus for themanufacture of microdevices such as semiconductor chips, liquid crystalpanels, CCDs or magnetic heads.

Semiconductor device manufacturing technology has recently advancedsignificantly and, along this, the fine processing technique has beenimproved considerably. Particularly, the optical processing techniquehas pressed the fine processing into a submicron region, withmanufacture of a device of 1-megabit DRAM. In many conventionallyadopted methods, for enhanced resolution, the numerical aperture (NA) ofan optical system is enlarged while keeping the exposure wavelengthfixed. Recently, however, it has been proposed and practiced to use anexposure wavelength of i-line in place of g-line, in an attempt toimprove the resolution in accordance with an exposure method using anultra-high pressure Hg lamp.

Along the advancement of using g-line or i-line as the exposurewavelength, the resist process itself has been advanced. Suchimprovements in the optical system and in the process together haveaccomplished rapid advancement of optical lithography.

Generally it is known that the depth of focus of a stepper is in inverseproportion to the square of the NA. It means that enhancing theresolution into a submicron order necessarily results in a problem ofdecreased depth of focus.

In consideration of this problem, many proposals have been made to useshorter wavelengths, as represented by an excimer laser, for enhancementof the resolution. It is known that the effect of using a shorterwavelength is in inverse proportion to the wavelength, and the shorterthe wavelength is, the deeper the depth of focus is.

On the other hand, independently of using light of shorter wavelength,many proposals have been made to use a phase shift mask (phase shiftmethod), in an attempt to improve the resolution. According to thismethod, a mask of conventional type is locally provided with a thin filmthat imparts, to light to be transmitted, a telecentric phase shift of80 deg. relative to the light incident on the remaining portion. Anexample has been proposed by Levenson of the IBM corporation. Here, ifthe wavelength is denoted by λ, the parameter is denoted by k₁ and thenumerical aperture is denoted by NA, then the resolution RP can be givenby:

    RP=k.sub.1 λ/NA

It is known that the parameter k₁, whose practical range is usuallytaken as 0.7-0.8, can be improved to about 0.35 with this phase shiftmethod.

There are many varieties of such phase shift methods, as referred to ina paper by Fukuda et al ("Nikkei Microdevices", July 1990, from page108).

An enhanced-resolution exposure method and apparatus is discussed in"Optical/Laser Microlithography V", SPIE Vol.1674, 1992, pages 91-104.In this system, for high-resolution projection, an illumination light(effective light source) is divided into four sections so as to providefour off-axis illumination lights.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvedillumination device. In one form of the invention, the illuminationdevice produces different illumination lights.

It is another object of the present invention to provide an exposureapparatus that uses such an illumination device.

It is a further object of the present invention to provide a microdevicemanufacturing method that uses such an illumination device.

In accordance with an aspect of the present invention, there is providedan illumination device, comprising: first and second optical integratorsdisposed along an optical axis and each having lens elements arrayed ina direction intersecting the optical axis; a condensing optical systemfor collecting light passed through said first and second opticalintegrators, to form a secondary light source; and means for relativelyshifting said second optical integrator relative to said first opticalintegrator, in a direction intersecting the optical axis.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a main portion of a first embodiment ofthe present invention.

FIG. 2 is an enlarged view of a portion of FIG. 1.

FIG. 3 is an enlarged view of a portion of FIG. 1.

FIGS. 4A-4C are schematic views for explaining light intensitydistributions on the light entrance surfaces of the optical integratorsof FIG. 2.

FIGS. 5A-5C are schematic views for explaining light intensitydistributions on the light entrance surfaces of the optical integratorsof FIG. 3.

FIG. 6 is a schematic view of a modified form of the FIG. 3 example.

FIGS. 7A-7C are schematic views for explaining light intensitydistributions on the light entrance surfaces of the optical integratorsof FIG. 6.

FIG. 8 is an enlarged view of a portion of FIG. 1.

FIG. 9 is a schematic view for explaining the paraxial refractive powerarrangement of the elements of FIG. 2.

FIGS. 10A-10C are schematic views for explaining light intensitydistributions on the light entrance surfaces of the optical integratorsof a second embodiment of the present invention.

FIGS. 11A-11C are schematic views for further explaining light intensitydistributions on the light entrance surfaces of the optical integratorsof a second embodiment of the present invention.

FIG. 12 is a schematic view of a portion of a third embodiment of thepresent invention.

FIGS. 13A-13C are schematic views for explaining light intensitydistributions on the light entrance surfaces of the optical integratorsof FIG. 12.

FIGS. 14A and 14B are schematic views of prisms usable in the presentinvention.

FIGS. 15A and 15B are schematic views for explaining a portion of afourth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, a first embodiment of the present inventionwill be explained. Denoted at 2 is an elliptical mirror, and denoted at1 is a light emitting tube (light source) which includes ahigh-luminance light emitting portion 1a for emitting ultraviolet raysand deep-ultraviolet rays, for example. The light emitting portion 1a isdisposed adjacent to the first focal point of the elliptical mirror 2.Denoted at 3 is a cold mirror which is provided with a multilayered filmeffective to transmit most of infrared rays but to reflect most ofultraviolet rays. The elliptical mirror 2 cooperates with the coldmirror 3 to form an image (light source image) 1b of the light emittingportion 1a, in the neighborhood of the second focal point 4.

Denoted at 5 is an optical system (lens system) for projecting lightfrom the light emitting portion image 1b upon the light entrance surface6a of a first optical integrator 6. The optical system 5 serves to placean opening 2a of the elliptical mirror 2 and the light entrance surface6a of the first optical integrator, in an optically conjugate relation.As shown in FIG. 8, the first optical integrator 6 comprises smalllenses 6i (i=1 to N) arrayed two-dimensionally at a predetermined pitchP. As shown in FIG. 2, it serves to form a secondary light source at apredetermined position (adjacent to the light entrance surface 7a of asecond integrator 7, to be described) in the neighborhood of the lightexit surface 6b.

Denoted at 7 is the second optical integrator which comprises smalllenses 7i (i=1 to M (M>N)) arrayed two-dimensionally at the same pitch Pof the small lenses of the first optical integrator 6. The secondoptical integrator 7 serves to project the light coming from thesecondary light source formed on its light entrance surface 7a, from itslight exit surface 7b in the form of substantially parallel light.

Denoted at 20 is a changing means for displacing at least one of thefirst and second optical integrators, to change the positionalrelationship between the small lenses of these optical integrators.

Denoted at 8 is a first condensing lens for collecting the light fromthe second optical integrator 7 and for projecting it on a third opticalintegrator 9. The secondary light source formed on the light entrancesurface 7a of the second optical integrator 7 by the first opticalintegrator 1, is imaged on the light entrance surface 9a of the thirdoptical integrator 9 by means of the second optical integrator 7 and thefirst condensing lens 8. On the light exit surface 9b of the thirdoptical integrator 9, a secondary light source (image) having a lightintensity distribution corresponding to that defined on the lightentrance surface 9a of the third optical integrator 9 is formed.

In this embodiment, the elements 7 and 8 are so set that the lightentrance surface 7a of the second optical integrator 7 and the lightentrance surface 9a of the third optical integrator 9 are placedsubstantially in a conjugate relation.

Also, in this embodiment, the elements 6, 7, 8, and 9 are so set thatthe light entrance surface 6a of the first optical integrator 6, thelight exit surface 7b of the second optical integrator 7 and the lightexit surface 9b of the third optical integrator 9 are placedsubstantially in a conjugate relation.

Denoted at 10 is a stop member having openings, which is disposedadjacent to the light exit surface 9b of the third optical integrator 9.The stop member 10 is so arranged that its opening shape on the lightpath can be changed. This assures the changeability of the shape of thesecondary light source 10a to be formed at the position of the stopmember 10.

Denoted at 11 is a half mirror. Most of the light from the stop member10 is reflected by this half mirror 11. The remaining light passesthrough the half mirror 11 and is received by a photodetector 12.Denoted at 13 is a second condensing lens for collecting the lightreflected by the half mirror 11, to illuminate a circuit pattern of areticle 14 surface (surface to be illuminated) placed on a reticle stage15.

Denoted at 16 is a projection optical system for projecting, in areduced scale, the circuit pattern on the reticle 14 surface onto thesurface of a wafer 17 placed on a wafer chuck 18. Here, the secondarylight source 10a adjacent to the light exit surface 9b of the opticalintegrator 9 is imaged by the second condensing lens 13 on the pupil 16aof the projection optical system 16. Denoted at 19 is a wafer stage onwhich the chuck 18 is mounted.

In this embodiment, in accordance with the orientation and linewidth,for example, of the circuit pattern of the reticle 14, one of the stateof FIG. 2 (normal illumination) and the state of FIG. 3 (off-axisillumination) wherein the second optical integrator 7 is displacedperpendicularly to the optical axis, is selected. The selection is madeby using the changing means 20. As required, the positions of theoptical system 5 and the first condensing lens and/or the aperture shapeof the stop member 10 may be changed. This is done to change the lightintensity distribution of the secondary light source image to be formedon the pupil plane 16a of the projection optical system 16.

The photodetector 12 comprises a sensor array (e.g. a CCD array). Itreceives the light transmitted through the half mirror 11, and itmonitors the quantity of light impinging on the reticle 14 as well asthe shape (light intensity distribution) of the secondary light source10a formed adjacent to the light exit surface 9b of the third opticalintegrator 9.

Now, the features of the optical arrangement from the first opticalintegrator 6 up to the third optical integrator 9 of this embodimentwill be explained.

As shown in FIG. 2, the focal point positions of the small lenses 6i atthe exit (rear) side of the first optical integrator 6 and the focalpoint positions of the small lenses 7i at the entrance (front) side ofthe second optical integrator 7 are approximately coinciding along theplane B. The plane B approximately coincides with the light entrancesurface 7a of the second optical integrator 7. Plane A corresponds tothe light entrance surface 6a of the first optical integrator, and planeC corresponds to the light entrance surface 9a of the third opticalintegrator 9. The light entrance surface 6a of the first opticalintegrator 6 and the focal point positions of the small lenses 6i at theentrance side of the integrator 6 are approximately coinciding, whilethe light exit surface 7b of the second optical integrator 7 and thefocal point position D of the small lenses 7i at the exit side of theintegrator 7 are approximately coinciding.

Now, it is assumed that the small lens 6i has a focal length f1, thesmall lens 7i has a focal length f2 and the first condensing lens 8 hasa focal length F1.

FIG. 9 schematically shows the paraxial arrangement of the opticalsystem, from the light entrance surface 6a (plane A) of the firstoptical integrator 6 to the light entrance surface (plane C) of thethird optical integrator 9.

In this embodiment, the relation f1≧f2 is satisfied so as to assure thatthe light incident on the first optical integrator 6 is projected on thesecond optical integrator 7 and exits therefrom, without being eclipsedby the side face of the small lens 6i.

In this embodiment, by using the changing means 20, the second opticalintegrator 7 is displaced perpendicularly to the optical axis(translationally deviated) to change the light intensity distribution(secondary light source) on the light entrance surface 9a of the thirdoptical integrator 9, to thereby change the light intensity distributionof the secondary light source image formed in the neighborhood of thepupil plane 16a of the projection optical system 16. Here, the lightintensity distribution on the light entrance surface 9a of theintegrator 9 is changed, from a substantially uniform distribution to adistribution wherein the intensity is higher in the off-axis area thanin the on-axis area. Also, the light intensity distribution of thesecondary light source image adjacent to the pupil plane 16a is changed,from a substantially uniform distribution to a distribution wherein theintensity is higher in the off-axis area than in the on-axis area. Theoptical action in such an intensity distribution change will now beexplained.

In this embodiment, by means of the optical system 5, an image of theopening 2a of the elliptical mirror 2 is formed on the light entrancesurface 6a of the first optical integrator 6. Thus, the light intensitydistribution on the light entrance surface 6a of the integrator 6 has ahigher intensity area as depicted by hatching in FIG. 4A. The manner ofillustration applies to the remaining drawings. The grid as depicted bybroken lines in FIG. 4A represents the array of the small lenses 6i.

Each small lens of this embodiment has a square sectional shape. When asshown in FIG. 2 the small lenses of the first optical integrator 6 andthe small lenses of the second optical integrator 6 are placed in acoaxial relation and do not have eccentricity (i.e. the state of normalillumination), the light source images are formed by the first opticalintegrator 6 on the light entrance surface 7a of the second opticalintegrator 7 such as shown in FIG. 4B. The grid depicted by broken linesin FIG. 4B represents the array of the small lenses 7i of the secondoptical integrator 7.

By means of the small lenses 7i and the first condensing lens 8, thelight source images formed on the light entrance surface 7a of theintegrator 7 are then superposed one upon another, on the light entrancesurface 9a of the third optical integrator 9 such as shown in FIG. 4C.The light intensity distribution of FIG. 4C thus defined is close to aGaussian distribution. The grid as depicted by broken lines in FIG. 4Crepresents the array of the small lenses 9i (i=1 to N) of the thirdintegrator 9.

The light intensity distribution defined on the light entrance surface9a of the integrator 9 determines the light intensity distribution ofthe effective light source (secondary light source) to be formed on thepupil plane 16a of the projection optical system 16. As a result, theeffective light source formed on the pupil plane 16a of the projectionoptical system has a light intensity distribution close to a Gaussiandistribution. The manner of illumination using such a light intensitydistribution (i.e. normal illumination) is to be used in cases where thecircuit pattern of the reticle 14 has a relatively large linewidth.

If the linewidth of the circuit pattern of the reticle 14 is relativelysmall and a high resolution is required, by using the changing means 20the second optical integrator 7 is shifted relative to the first opticalintegrator 6, as shown in FIG. 3, in a direction perpendicular to theoptical axis and by an amount corresponding to a half of the pitch ofthe small lenses 7i (i.e. by a half pitch in a direction of anorthogonal array of the small lenses). It is to be noted that as shownin FIG. 5A the light intensity distribution on the light entrancesurface 6a of the integrator 6 is the same as that of FIG. 4A.

As shown in FIG. 5B, by means of the optical integrator 6, light sourceimages are formed on the light entrance surface 7a (plane B) of thesecond optical integrator 7. As seen from FIG. 5B, on the light entrancesurface 7a of the integrator 7 each light source image is formed whilepartially covering four small lenses. As a result, each light sourceimage is divided into four. By means of the first condensing lens 8, thethus divided light source images are superposed on the light entrancesurface 9a (plane C) of the third optical integrator 9 such as shown inFIG. 5C.

In this embodiment, a secondary light source image corresponding to thelight intensity distribution with quadruplex peaks is formed on thepupil plane 16a of the projection optical system 16, and high-resolutionillumination is made in this manner. In accordance with thisillumination method, the circuit pattern of the reticle 14 is projectedand transferred by the projection optical system 16 onto the wafer 17surface. Through subsequent various processes such as a developingprocess, semiconductor devices are produced.

In this embodiment, in the high-resolution illumination state shown inFIG. 3, by using the changing means 20 the distance between the firstand second optical integrators 6 and 7 along the optical axis may alsobe changed to adjust the intensity distribution of the secondary lightsource or the effective light source.

FIG. 6 is a schematic view for explaining the elements 6, 7, 8 and 9 inthis case. In FIG. 6, while light source images are formed on the lightentrance surface 7a of the second optical integrator 7 by means of thefirst optical integrator 6, these light source images are defocused suchas depicted in FIG. 7B, as compared with the case of FIG. 5B. FIG. 7Ashows the light intensity distribution on the light entrance surface 6aof the integrator 6, and this is the same as that of FIG. 5A. Also, onthe light entrance surface 9a of the third optical integrator 9, theformed light intensity distribution has expanded quadruplex peaks ascompared with the case of FIG. 5C.

In this manner, the spacing between the first and second opticalintegrators 6 and 7 along the optical axis may be changed fro the FIG. 3state, to adjust the light intensity distribution (effective lightsource) to be formed on the pupil plane 16a of the projection opticalsystem 16.

Also, in this embodiment, in the high-resolution illumination state ofFIG. 3 the disposition of the first condensing lens 8 may be changed(first condensing lens 8') and the imaging magnification of the lightentrance surface of the small lenses 7i (i=1 to M) of the second opticalintegrator and the light entrance surface of the third opticalintegrator may be changed.

FIG. 12 shows the elements 6, 7, 8'and 9 in such a case. FIG. 13A showsthe light intensity distribution on the light entrance surface 6a of thefirst optical integrator 6, which is the same as that of FIG. 5B. Thelight intensity distribution to be formed in this case on the lightentrance surface 9a of the third optical integrator 9 corresponds tothat of FIG. 5C as magnification-changed (reduced), such as depicted inFIG. 13C.

Further in this embodiment, in the high-resolution illumination state ofFIG. 3, prisms 21 and 22 shown in FIG. 14 may be disposed in front ofthe third optical integrator 9 such as shown in FIG. 15A. On thatoccasion, by changing the spacing between the prisms 21 and 11, thelight intensity distribution on the light entrance surface 9a of thethird integrator 9 may be changed such as shown in FIG. 15B.

In this embodiment, in place of displacing the second optical integrator7 in a direction perpendicular to the optical axis for establishing thehigh-resolution illumination, the first optical integrator 6 may bemoved in a direction perpendicular to the optical axis. Further, theamount of displacement (eccentricity) is not limited to the half pitchof the small lenses of the first and second optical integrators. Adesired amount of eccentricity may be adopted to adjust the effectivelight source distribution as desired. On that occasion, the effectivelight source distribution may be adjusted while monitoring it throughthe-photodetector 12 of FIG. 1, for example.

FIGS. 10A-10C and FIGS. 11A-11C are schematic views for explaining thelight intensity distribution on the light entrance surface of theoptical integrators, in the normal illumination state and thehigh-resolution illumination state in a second embodiment of the presentinvention.

Basic structure of this embodiment is similar to the embodiment of FIG.1 but, as a difference, the light source image 1b is imaged by theoptical system 5 on the light entrance surface 6a of the first opticalintegrator 6.

FIGS. 10A, 10B and 10C show the light intensity distributions on thelight entrance surfaces 6a, 7a and 9a of the first, second and thirdoptical integrators 6, 7 and 9, respectively, in the normal illuminationstate (corresponding to the state of FIG. 1).

FIGS. 11A, 11B and 11C show the intensity distributions on the lightentrance surfaces 6a, 7a and 9a of the first, second and third opticalintegrators 6, 7 and 9, respectively, in the high-resolutionillumination state (corresponding to the state of FIG. 3) wherein thepositional relationship between the small lenses of the first and secondoptical integrators 6 and 7 is changed.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

What is claimed is:
 1. An exposure apparatus a comprising:light sourcemeans; first, second and third optical integrators disposed along anoptical axis, for receiving light from said light source means, each ofsaid first to third optical integrators having lens elements arrayed ina direction perpendicular to the optical axis; a first condensingoptical system for directing, onto said third optical integrator, lightpassed through said first and second optical integrators, to form asecondary light source through said third optical integrator; means forrelatively shifting said second optical integrator relative to saidfirst optical integrator, in the direction perpendicular to the opticalaxis; a second condensing optical system for receiving light from saidsecondary light source and directing the light to a mask; and aprojection optical system for projecting an image of a pattern of themask, irradiated with the light from said secondary light source, onto asubstrate.
 2. An apparatus according to claim 1, wherein said lenselements of said first and second optical integrators are arrayed at thesame pitch, and wherein said shifting means shifts said second opticalintegrator selectively between a first state in which said lens elementsof said first and second optical integrators are placed coaxially and asecond state in which said lens elements of said first and secondoptical integrators are relatively deviated by a half of said pitch. 3.An apparatus according to claim 2, wherein the lens elements of saidsecond optical integrator and the lens elements of said third opticalintegrator are arrayed at the same pitch.
 4. An apparatus according toclaim 1, wherein said first condensing optical system includes prismmeans demountably insertable into a path of the light.
 5. An apparatusaccording to claim 1, wherein said first condensing optical systemincludes a variable-magnification optical system.
 6. An apparatusaccording to claim 1, wherein each of said lens elements of each of saidfirst and second optical integrators has a square sectional shape.
 7. Anapparatus according to claim 6, wherein each of the lens elements ofsaid third optical integrator has a rectangular sectional shape.
 8. Anapparatus according to claim 1, wherein said shifting means shifts saidsecond optical integrator relative to said first optical integrator inthe direction perpendicular to the optical axis, and wherein saidshifting means changes the distance between said first and secondoptical integrators in the optical axis direction.
 9. An apparatusaccording to claim 1, wherein said light source means includes a lightemitting portion, an elliptical mirror for reflecting light from saidlight emitting portion, and an imaging lens system for directing lightreflected by said elliptical mirror to said first optical integrator,and wherein said imaging lens system images said light emitting portionon said first optical integrator.
 10. An apparatus according to claim 1,wherein said light source means includes a light emitting portion, anelliptical mirror with an opening, for reflecting light from said lightemitting portion, and an imaging lens system for directing lightreflected by said elliptical mirror to said first optical integrator,and wherein said imaging lens system images said opening of saidelliptical mirror on said first optical integrator.
 11. An apparatusaccording to claim 1, further comprising a variable stop disposedadjacent to a light exit surface of said third optical integrator, forchanging the shape of said secondary light source.
 12. An apparatusaccording to claim 1, wherein a light entrance of said first opticalintegrator is optically conjugate with a light exit surface of saidsecond optical integrator, and a light entrance surface of said secondoptical integrator is optically conjugate with a light entrance surfaceof said third optical integrator.
 13. A device manufacturing methodwherein light passed through first and second lens arrays, which aredisposed along an optical axis, form a secondary light source andwherein a device pattern is illuminated with light from the secondarylight source whereby the device pattern is transferred to a substrate,said method comprising the steps of:illuminating a first pattern withthe secondary light source, while aligning optical axes of the first andsecond lens arrays with each other in a direction perpendicular to theoptical axis; and obliquely illuminating a second pattern, finer thanthe first pattern, with the secondary light source while deviating theoptical axes of the first and second lens arrays from each other, in thedirection perpendicular to the optical axis.
 14. A device manufacturingmethod wherein light passed through first and second lens arrays, whichare disposed along an optical axis, form a secondary light source andwherein a device pattern is illuminated with light from the secondarylight source whereby the device pattern is transferred to a substrate,said method comprising the steps of:forming the secondary light source,while deviating optical axes of the first and second lens arrays fromeach other, in a direction perpendicular to the optical axis; andobliquely illuminating the device pattern with the formed secondarylight source.